DEVELOPMENT OF THE ENAMEL 171 



regularly arranged within the enamel organ and extend from 

 the circumference to its free inner surface. 



While the stellate reticulum probably serves as a store- 

 house of material for the commencement of calcification, 

 the cells of the stratum intermedium play, according to 

 many authors, the most important role in the selection of 

 material from the blood for the completion of the process. 



The ameloblast cells which constitute the internal epithe- 

 lium of the enamel organ are the active agents in the elabora- 

 tion of the calcifying products. 



They contain clear oval bodies which are considered to 

 consist of the colloidal material which is separated by them. 



When calcification has commenced, a separating mem- 

 brane is seen between the stratum intermedium and the 

 internal epithelium and another between the cells of the 

 internal epithelium and the forming enamel. These are 

 called the external and internal ameloblastic membranes 

 respectively. 



Each ameloblast is furnished with a process or prolonga- 

 tion of a fibrillar nature the Tomes' process. These pro- 

 cesses pass from the ends of the ameloblasts to the forming 

 enamel, and are incorporated in its substance, forming with 

 other transversely arranged fibres the organic network 

 or foundation substance of the enamel. This is most 

 evident in marsupial enamel, but the same structure exists 

 in other mammalian enamels, although it is much earlier 

 veiled by dense calcification. Decalcification experiments 

 confirm the existence of a fibrillar basis substance after the 

 removal of the lime salts in marsupial enamel. This organic 

 residue is derived from the ameloblast cells.. It is within the 

 substance of the longitudinal fibres 'or prolongations of the 

 Tomes' processes that the calcification of the enamel prisms 

 takes place. 



The honeycomb is a fenestrated membrane-like substance 

 seen in the outer part of the forming enamel to which 

 the fibres of the Tomes' processes pass, and, according to 

 C. S. Tomes, the fibres enter the interspaces and are attached 

 to the septa. This honeycomb is considered by Tomes to 

 be identical with the fenestrated membrane raised from 

 the surface of forming enamel by acids ; it also sometimes 



